(Bug 4805) Don't enforce the same rules for posting and editing

These three error messages were update-specific and shouldn't affect
editing (for example imported communities may have entries by openid
users). So let's move this checking up from _init, which is called from
/new and /edit, and into just /new.
Merge pull request #194 from afuna/openid-new-edit-bug4805

(Bug 4805) Don't enforce the same rules for posting and editing